Method and composition for neutralizing acidic components in petroleum refining units

Abstract

A method of inhibiting corrosion and fouling in petroleum refining units which comprises adding choline hydroxide either alone or in combination with a hydrogen-bond donor such as a carboxylic acid, an amine, an amide, or an alcohol.

Claims

1. A process for neutralizing acidic components in a distillation overhead system of a refining unit comprising water condensate and petroleum products, the process comprising: adding to the distillation overhead system a neutralizing amount of a neutralizing composition comprising an aqueous solution of choline hydroxide and an hydrogen-bond donor, the hydrogen bond donor being glycerol, the distillation overhead system including an overhead line off of a distillation column and the neutralizing composition being added in the overhead line.

2. The process of claim 1 wherein the choline hydroxide and the hydrogen bond donor are mixed together prior to being added.

3. The process of claim 1 wherein the solution of choline hydroxide and the hydrogen bond donor are added to the system separately.

4. The process of claim 1 further comprising the step of adding one or more alkylamine or alkanolamine.

5. The process of claim 4 wherein the alkylamine or alkanolamine is dimethylethanolamine (DMEA), dimethylisopropanolamine (DMIPA), ethylenediamine (EDA), methoxypropylamine (MOPA), monoethanolamine (MEA), dimethylaminopropylamine (DMAPA), morpholine, or trimethylamine (TMA).

6. The process of claim 1 wherein the amount of the neutralizing composition ranges from 1 to 10,000 ppm based on the petroleum products.

7. The process of claim 1 further comprising the step of adding the neutralizing composition to the system at a rate sufficient to maintain the pH of water condensate in the system at a pH of equal to or greater than 4.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Methods and compositions are disclosed for neutralizing acid environments in distillation overhead systems of petroleum product processing facilities, including, but not limited to distillation columns, vacuum distillation columns, preflash towers, and the like. The neutralizer composition comprises an aqueous and/or organic solution of choline hydroxide.

(2) For decades, refiners have struggled with providing adequate neutralization in overhead systems without forming corrosive salts Ammonia and several amines have been tried to control corrosion with random successes and failures. The neutralizer compositions of the invention will allow greater neutralization of corrosive acids in column overhead condensing systems without increasing the potential to form corrosive salts with hydrogen chloride.

(3) The water vapor/condensate coming out of the overhead of the crude distillation unit (CDU) in the refinery is very acidic primarily due to the presence of acidic components, such as hydrochloric acid (HCl), which is formed when the crude oil passes through a heating furnace (composed of metal chlorides such as MgCl.sub.2, CaCl.sub.2, etc.) prior to entering the CDU. Water vapor and HCl rise to the top of the distillation tower along with the light components of the crude oil such as liquefied petroleum gas and naphtha. This stream passes through an overhead line and then enters a condenser, after which the water stream will be separated from naphtha and off-gas and sent to a water treatment unit. The acidic HCl stream (often having a pH less than 2) is highly corrosive and needs to be neutralized (preferably to a pH of 4 or greater, more preferably 5 or greater). The neutralizing composition is added to the overhead system, traditionally, neutralizers are injected into the overhead system between the CDU and the condenser.

(4) The neutralizing compositions of the present invention bind the hydrogen ions thus reducing their concentration. In one embodiment of the present invention, the neutralizing composition may be added to the overhead system upstream of the aqueous dew point. This addition point is usually the overhead line off of the distillation column or the vapor line off of a dry first condensing stage accumulator.

(5) It will be appreciated that it is not necessary for corrosion in distillation overheads or other equipment to completely cease for the method of this invention to be considered successful. Indeed, the inventive method should be considered operative if corrosion is inhibited to a measurable extent. In the context of this invention, the term corrosion inhibition is defined to include any cessation, prevention, abatement, reduction, suppression, lowering, controlling or decreasing of corrosion, rusting, oxidative decay, etc. Similarly, the term neutralize refers to such corrosion inhibition by reducing the acidity of the chemicals or components in the system such as by raising pH, but does not require adjusting pH to be 7, but rather raising of pH and moving from acidity to basicity to some measurable extent. Furthermore, the nature of the metal surfaces protected in the methods of this invention is not critical. The metals in which the system operates may include, but are not necessarily limited to iron alloys, copper alloys, nickel alloys, titanium alloys, and these metals in unalloyed form as well, etc.

(6) In one embodiment of the present invention the neutralizing composition is an solution comprising choline hydroxide. The solution solvent may be water, i.e., an aqueous solution, an organic solvent, or mixtures thereof. Suitable organic solvents are alcohols, amines, and ethers, for example glycol and glycol ether. In another embodiment of the present invention the neutralizing composition is an aqueous mixture consisting of only water and choline hydroxide. We believe that when the choline hydroxide encounters HCl in an aqueous environment it is converted to choline chloride which raises the pH in the system.

(7) In a preferred embodiment of the present invention, in addition to the neutralizing composition comprising choline hydroxide, one or more hydrogen-bond donor (HBD) such as carboxylic acids, amines, amides, or alcohols is added to the overhead system. Examples of suitable HBDs are glycerol, ethylene glycol, urea, acetamide, thiourea, m-cresol, and phenol. In one embodiment of the present invention, the choline hydroxide and the one or more HBD are mixed together as a solution prior to being added to the overhead system of the distillation unit. In another embodiment of the present invention, the choline hydroxide solution and the one or more HBD are added separately to the overhead system of the distillation unit.

(8) A deep eutectic solvent is formed by complexing an ammonium compound (e.g., choline chloride) with an HBD. The melting point of a deep eutectic solvent is lower than each of the melting points of the compounds that form it. We believe that when one or more HBD is present in the system in the presence of choline hydroxide in the presence of HCl, an eutectic solvent is formed. These liquids have physical and solvent properties that are similar to ionic liquids formed from discrete ions.

(9) The choline hydroxide is present in the solution in an amount equal to or greater than 1 weight percent to an amount equal to or less than 99.9 weight percent. Preferably, the choline hydroxide is present in the solution in an amount equal to or greater than 1 weight percent, more preferably in an amount equal to or greater than 2 weight percent, more preferably in an amount equal to or greater than 3 weight percent, more preferably in an amount equal to or greater than 5 weight percent, and most preferably in an amount equal to or greater than 10 weight percent. Preferably, the choline hydroxide is present in the solution in an amount equal to or less than 99.9 weight percent, more preferably in an amount equal to or less than 90 weight percent, more preferably in an amount equal to or less than 85 weight percent, more preferably in an amount equal to or less than 80 weight percent, and most preferably in an amount equal to or less than 50 weight percent.

(10) The choline hydroxide to HBD ratio, whether added mixed together or separately, is from 1:2 to 10,000:1. For example, when the HBD is pre-mixed in the solution, it is present in an amount equal to or greater than 0.1 weight percent, more preferably in an amount equal to or greater than 1 weight percent, more preferably in an amount equal to or greater than 2 weight percent, more preferably in an amount equal to or greater than 5 weight percent, and most preferably in an amount equal to or greater than 10 weight percent. Preferably, when the HBD is pre-mixed in the solution it is present in an amount equal to or less than 67 weight percent, more preferably in an amount equal to or less than 50 weight percent, more preferably in an amount equal to or less than 40 weight percent, more preferably in an amount equal to or less than 30 weight percent, and most preferably in an amount equal to or less than 20 weight percent.

(11) It will be appreciated that it is difficult to predict what the optimum dosage rate would be in advance for any particular system. The dosage will depend upon a variety of complex, interrelated factors including, but not necessarily limited to, the exact nature of the stream being fractionated, the temperature and pressure of the distillation conditions, the particular amine blends used, etc. In one non-limiting embodiment of the invention, the dosage rate will be determined on a case-by-case basis depending upon the acid content of the system. It may be desirable to use computer modeling to determine the optimum rate. Nevertheless, to provide some understanding of expected or possible dosage rates, the amount of neutralizing composition may range from 1 to 10,000 ppm, based on the petroleum products. In another non-limiting embodiment, the amount of neutralizing composition may range from 2 to 500 ppm.

(12) The desired pH range for all points in the system is from 4 to 8.5, and in another non-limiting embodiment may be from 5 to 7. Alternatively, to give another idea of expected dosage rates, the neutralizing composition may be added to the system at a rate sufficient to maintain the pH of water condensate in the system at a pH of equal to or greater than 4.0. In another non-limiting embodiment, the neutralizing composition may be added to the system at a rate sufficient to maintain the pH of equal to or greater than 5.0.

(13) The neutralizing composition of the present invention may further comprise one or more alkylamine or alkanolamine, preferably dimethylethanolamine (DMEA), dimethylisopropanolamine (DMIPA), ethylenediamine (EDA), methoxypropylamine (MOPA), monoethanolamine (MEA), dimethylaminopropylamine (DMAPA), morpholine, and trimethylamine (TMA). If present, the one or more alkylamine or alkanolamine is added in an amount of from 1 to 1000 ppm based on the petroleum products.

EXAMPLES

(14) The choline hydroxide is purchased from Aldrich as 20 wt % aqueous solution. The glass apparatus is fabricated by Scientific Glass & Plastic, Inc. The NE-300 Just Infusion Syringe Pump is purchased from New Era Pump Systems Inc. The pH value is monitored by an Orion 720A+ pH meter from Thermo Electron Corporation.

(15) The experimental setup is set up to mimic a CDU. To a 250 mL round bottle is loaded 35% HCl solution with stirring. The bottle is connected to an H-tube with a side sample injection port. The H-tube is further connected with a thermometer, a buffer bottle and a U-tube. The other side of the U-tube is immersed in 50 mL water, the pH value is monitored by the pH meter. A heating mantle is used to boil off HCl. The neutralizer is spray-injected through the side port of the H-tube via a syringe and the injection rate is controlled by the syringe pump. Three experiments are conducted: Comparative Example A, no neutralizer, Comparative Example B, a 5 wt % solution of monomethanolamine, a widely used CDU neutralizer, and Example 1, a 5 wt % aqueous mixture of choline hydroxide with 1 wt % glycerol in water.

(16) The HCl solution is heated to 120 C. and the neutralizer is added at a constant speed by the syringe pump through the sprayer when the pH value of the gas in the outlet starts to drop, to simulate a neutralizer injection on top of a CDU. Upon heating, HCl evolves from the round bottle flask and eventually is dissolved by water in the beaker or neutralized by the neutralizer and stays in the buffer bottle in the form of chloride salt. The pH value of the water in the beaker is indicative of the neutralization efficiency. The pH of the vapor in the outlet is monitored by a pH meter. Table 1 shows the pH value change of the water in the beaker versus time.

(17) TABLE-US-00001 TABLE 1 Time, minutes Com Ex A Com Ex B Ex 1 1 5.9 5.9 5.9 2 5.8 5.8 5.8 3 5.7 5.7 5.7 4 5.4 5.0 5.2 5 5.3 4.8 5.2 6 5.2 4.8 5.1 7 5.1 4.8 5.1 8 5.0 4.5 5.0 9 5.0 4.3 5.0 10 3.5 4.1 4.5 11 2.8 4.0 4.4 12 2.1 4.0 4.4 13 1.8 4.0 4.2 14 1.6 4.0 4.2 15 1.3 4.0 4.2

(18) Without neutralizer, the pH value of the water decreased slowly to around 4.0 in the first 10 minutes and dropped dramatically and quickly afterwards, suggesting HCl started to evolve rapidly at that point, consistent with the temperature rise observed on top of the HCl solution in the round bottle. The neutralizer compositions, Comparative Example B and Example 1, are spray-injected after the round bottle is heated for 10 minutes as well. As can be seen, the pH value stayed above 4.0 during the course of the experiments. No solid deposition is observed. The experimental data suggests that choline hydroxide effectively neutralizes HCl vapor.

Example 2

(19) The viscosity of a mixture of ethylene glycol and choline chloride in a 2:1 mole ratio is measured in an Anton Paar SVM 3000/G2 Stabinger Viscometer at various temperatures. As shown in Table 2, the viscosity of this mixture is below 30 cP at 20 C. and is 3.36 cP at 100 C.

(20) TABLE-US-00002 TABLE 2 Temperature, C. Dynamic viscosity, cP 20 29.00 30 19.70 40 13.97 50 10.31 60 7.86 70 6.16 80 4.94 90 4.04 100 3.36